Recently, miniaturization of electronic machines has been bringing a demand for development of small-sized capacitors having a large capacity.
As one of such capacitors having a large capacity, solid electrolytic capacitors with a high capacitance, using as a dielectric material an amorphous niobium oxide whose electrical insulation is high and dielectric constant is 1.8 times higher than that of tantalum oxide of a material used for conventional solid electrolytic capacitors, have been focused on.
Unfortunately, the conventional solid electrolytic capacitors using niobium oxide as the dielectric material have problems that they are easily affected by heat-treatment, such as a reflow soldering process and their capacitance stability is easily deteriorated compared with solid electrolytic capacitors using another dielectric materials such as tantalum oxide.
In order to solve such a problem, there has been proposed a solid electrolytic capacitor in which a dielectric layer is composed of niobium oxide wherein a niobium nitride region is formed (for example, see Japanese Published Unexamined Patent Application No.11-329902).
However, even in such a solid electrolytic capacitor in which the dielectric layer is composed of niobium oxide wherein the niobium nitride region is formed, one part of the amorphous niobium oxide is crystallized by the heat-treatment, such as the reflow soldering process. As a consequence, a crystal of niobium oxide with a decreased electrical insulation is contained in the dielectric layer, and the electrical insulation of the dielectric layer is decreased.
Further, volume change occurs in niobium oxide in accordance with change of state thereof from being amorphous to crystal. Then, a crack in the dielectric layer is easily occurred due to crystallization of niobium oxide. Thus, there has been a problem that short circuit between an anode and a cathode formed on the surface of the dielectric layer is easily occurred.
Still further, the solid electrolytic capacitor in which the dielectric layer is composed of niobium oxide wherein the niobium nitride region is formed has problems that diffusion of oxygen is not fully suppressed and thickness of the dielectric layer is easily decreased.
As a consequence, a problem with the conventional solid electrolytic capacitors has been that it impossible to sufficiently reduce leakage current between the anode and the cathode.